1. Field of the Invention
The present invention relates to an information server which has a function of storing information and serves the stored information in response to a request from a terminal. The present invention also relates to a communication apparatus that is connected to a local-area network and a wide-area network.
2. Related Art Statement
Generally, a communication band of the Internet is narrower than that of an in-company network. Therefore, when information is served to both the Internet and the in-company network, two servers are used, that is, a first server that holds one or more files suitable for the Internet, and a second server that holds one or more files suitable for the in-company network, and each file for the Internet is reduced in size as compared with each file for the in-company network (for example, a resolution of an image represented by a file for the Internet is lowered as compared with that of an image represented by a file for the in-company network).
However, the use of two servers leads to increasing the cost of hardware. This problem may be solved by a method disclosed by, e.g., Japanese Patent Application Publication No. 2002-217965 or its corresponding U.S. patent application Publication No. 2003/0212892A1. In this method, an information server as an addresser measures a bandwidth of a transmission line between the server and a communication apparatus as an addressee, selects a codec corresponding to the measured bandwidth, and transmits information using the selected codec.
However, in the case where the method disclosed by the above-indicated patent document is applied to a single server that is connected to two communication lines or networks, e.g., a WAN (wide-area network) and a LAN (local-area network), the following problems may arise:
Though WAN has not only the problem that the bandwidth thereof is narrower than that of LAN, but also another problem that a security level (e.g., a degree of protection of information from tapping or modifying) of the transmission line of WAN is lower than that of LAN, those problems cannot be solved by the disclosed method. In addition, since the disclosed method needs to carry out the steps of dynamically measuring a bandwidth of a transmission line between the server and each one of a plurality of communication apparatuses and selecting a codec corresponding to the measured bandwidth, the overhead of communication needed to measure the bandwidth is not negligible, i.e., the loss of communication is so large that the method cannot be applied to a large-scale communication system.
Meanwhile, the Internet has been known as a wide-area network. As is well known in the art, the Internet Protocol (IP) is used in communicating with a computer (i.e., a communication apparatus or a terminal) connected to the Internet. Since, however, depletion of the address resources has become a serious problem, there is a plan to adopt a new internet protocol, i.e., IPv6 (the Internet Protocol version 6). According to this protocol, a plurality of IP addresses, e.g., a local IP address and a global IP address can be allotted to each terminal connected to the Internet.
Here, it can be assumed that a plurality of communication networks are constituted by a plurality of terminals to each of which a local IP address and a global IP address are allotted. When communication is carried out using a local IP address, a packet does not go out through a router connected to the Internet. Thus, a communication network that is located at a level lower than the router, functions as a local-area network. On the other hand, when communication is carried out using a global IP address, a packet goes out through the router. Thus, each terminal connected to the above-indicated local-area network also functions as a terminal connected to a communication network belonging to the Internet, i.e., a low-level network belonging to the Internet.
IPv6 has an additional feature that a protocol according to which each terminal can automatically determine its own addresses is integrated therewith. More specifically described, each communication apparatus that operates according to IPv6 can automatically determine a local IP address and a global IP address therefor, without waiting user's manual setting of the addresses, and thereby automatically connect the each apparatus itself to a local-area network and the Internet.
Since, however, a communication apparatus that operates according to IPv6 has a function of automatically connecting the apparatus itself to a wide-area network (i.e., the Internet), as described above, the apparatus may be detrimentally connected to a wide-area network (the Internet), against user's intention not to connect.
Here, it is assumed that a communication apparatus employs, e.g., a printer portion that is connected to the Internet. Generally, the printer portion is used in a local-area network only. However, in the case where the Internet is managed according to IPv6, it is needed to employ IPv6 as a communication protocol for the printer portion as well.
However, if the printer portion that operates according to IPv6 is connected to a local-area network located at a level lower than a router connected to a wide-area network (the Internet), the printer portion is automatically placed in a condition in which the printer portion can communicate with a terminal connected to the wide-area network located at a level higher than the router, so that the printer portion may be unfairly used by one or more persons other than one or more proper users.
Meanwhile, Japanese Patent Application Publication No. 2004-32699 discloses, as a method of restraining, in the environment of IPv6-managed networks, communications with persons other than proper users and protecting the privacy of the proper users, a method using a public key. According to this method, the above-indicated unfair use of the communication apparatus (e.g., the printer portion) can be prevented by using the public key.
However, the above-indicated method of using the public key to prevent the communications with the improper persons, has other problems that a great operation load is applied to the communication apparatus so as to deal with the public key and it is needed to provide an public key server in the IPv6-managed network.
If the printer portion is connected to an independent network that is physically isolated from a wide-area network, the printer portion can be used in the local-area network only, without needing to use the public key, while the unfair use of the printer portion by the terminals connected to the wide-area network can be prevented. However, recently, there has been known a printer portion having, e.g. a web-server function. That is, there has been known a printer portion having not only a function that is mainly aimed at use in a local-area network only, but also a function that is aimed at use in a wide-area network (the Internet). In this case, the printer portion cannot be physically isolated from the wide-area network.
Communications may be prevented by finding and discarding, with, e.g., a router, packets directed to one or more pre-selected terminals in a network. In this case, however, the management of the network becomes cumbersome and complicated.